Radio frequency (RF) receivers and transceivers can be found in numerous applications, particularly in the field of wireless communications and radar sensors. For example in the automotive sector, there is an increasing demand for radar sensors used in so-called “adaptive cruise control” (ACC) or “radar cruise control” systems. Such systems may be used to automatically adjust the speed of an automobile so as to maintain a safe distance from other automobiles ahead.
Modern radar systems make use of highly integrated RF circuits (MMICs, monolithic microwave integrated circuits), which may incorporate all core functions of an RF transmit and receive module (also referred to as “RF font-end”) of a radar transceiver in one single package (single chip transceiver). Such RF front-ends may include, inter alia, a voltage controlled oscillator (VCO), power amplifiers (PA), mixers, and analog-to-digital converters (ADC) and also a circulator or directional coupler.
One characteristic function of transmit and receive modules (RF front-ends) with one or more shared transmit and receive antenna is the separation of the strong transmit signal (TX) from the weak receive signal (RX). Traditionally, this function is implemented by passive devices (circulators, directional couplers), which
have large physical dimensions. Moreover, such passive devices usually exhibit undesired transmission losses. There is a need to replace the mentioned passive devices with active devices, which are a smaller in size and more efficient with regard to transmission losses.